Sheet metal drawing press



March 7, 1933. o. KUHNER SHEET METAL DRAWING PRESS Filed Sept. 23, 1931 2 Sheets-Sheet l March 7, 1933. v KUHNER 1,900,291

SHEET METAL DRAWING PRESS Filed Sept. 23, 1931 2 Sheets-Sheet 2 Fatented Mar. 7, 1933 OTTO K'lj'HNER, OF GOPPINGEN', GERMANY SHEET METAL DRAWING- PRESS Application filed September 2 3, 1931, Serial No. 564,635, and in Germany October 1, 1930.

This invention relates to a sheet-metal drawing press of that type in'which, during the drawing of the piece of sheet-metal, or of the blank respectively, that is to say, during that time in which the drawing punch is being moved downwardly and the blank is thereby drawn, the blank is located over a stamp and is held fast thereon between a v member (drawing ring or drawing stamp) moved by said punch and a holding ring or an equivalent holding member; and in which, simultaneously therewith, the respective holding member is moved counter to the resistance presented by a pad (preferably a compressedair pad) which moves that holding member later on into its initial position when the said punch is again being moved upwardly.-

There exists with such presses the'detrimental possibility that, owing to the movable 0 parts of said pad (in the following termed drawing device) quickly following the rising punch under the action of the compressed air or other counter-acting medium, the draw- 0 ing tool is subjected to detrimental blows, or that other drawbacks ensue.

In order to obviate said blows or other drawbacks it has already been proposed to provide a piston in a separate cylinder filled with a liquid and aflixed to the lower part of 39 the press table frame, the piston rod being secured to the movable part of the drawing device and being thus moved upwardly 'and downwardly together with the same. The r liquid present above said piston and the liquid present below the same communicate with one another through a pipe provided with a valve controlled by the main shaftof the press in such a manner that it is closed at the n endof the downward movement of the movv able parts of the drawing device and of the hydraulic piston whereby the flow or circulation of the liquid caused, prior thereto, by the downward movement of the piston is interr rupted and whereby, in consequence thereof, a is prevented that the movable drawing device members follow instantly the rising punch when this thereafter is again moved upwardly. Some time thereafter the valve is again opened by the control means pertaining thereto so that the ensuing: movement 'necting rod 6.

mentioned can now take place without any drawback.

The object of the invention is to attainthe same effect without the use of the separate hydraulic cylinder with its piston, that is to say, to present a by far simpler device. This is attained, according to this invention, by arranging the hydraulic locking cushion directly in the casing of the drawing device whereby the existing casing of said cushion may be utilized for housing the locking liq uid,-and the existing pressing piston, or one of the-existing pressing pistons of the drawing device, may be utilized for acting upon said locking'liquid. This is effected, on principle, in such a manner that the casin I part receiving and containing the locking liquid is connected up by means of a shutting-0E valve or the like controlled, for instance, from the main shaft of the press to a pipe leading to a collecting receptacle for the pressure liquid, and that now the piston which acts on thelocking liquid, or the casing part enclosing this piston, acts in such a manner that when the movable drawing device members are moved downwardly the locking liquid is sucked in, but cannot, after saiddownward movement has been finished and the shutting off valve is closed, escape whereby the movable parts of the drawing device are prevented from againbeing moved upwardly until the locking has been released by opening the said shutting-off valve. Q

The invention is illustrated diagrammatically and by way of example on the accompanying drawings on which Figure 1 is a complete front-view, partly in vertical, section, of a single-acting sheet-metal drawing press designed according to this invention. Figure 2 is a similar representation showing the lower half of a multiple press, the upper half being left away as unnecessary; and Figure 3 is a side-view of the upper part of Fig. 1, seen from the left.-

In Fig. 1, a denotes the drawing punch which reciprocates vertically by means of guide members 5 and 0 in the lateral'standards d of the press, and is actuated from the crank shaft f of the same by means of a con- To the lower end of'said -another suitable fluid under pressure.

punch is attached the drawing ring 9 which when the punch is moved downwardly draws the blank over the stationary drawing die or stamp m by means of the blank holding ring 2'. The drawing die m is affixed to the table 70 of the press. The holding ring 2' which embraces the die m is vertically shiftable there on and rests upon vertical rods n which are loosely slidable in the die m, these rods being supported on a press plate 0 resting in turn upon press rods 39 supported on a cylinder 9. This latter is located upon a piston 7- along which it can be reciprocated vertically and which is secured to the table of the-press by means of a piston rod 8. This rod has a transverse bore't and a longitudinal bore a, the lower end of which is in communication with. a vessel to containing compressed air or The drawing punch is shown in its highestposition. In this position of the punch the com pressed air presses the cylinder 9 upwardly until it contacts with the bottom surface of the table, and at the end of this movement the oil fills the receptacle 3 only partly, and

above'it is air either of atmospheric pressure or of a slightly higher pressure. A flexible pipe 4 also extending from the oil space of the receptacle 3 and connected at its other end with the cylinder space below the piston r is provided with a valve 5 that is controlled by means of a curved guide groove 10, 10 in a fly-wheel 11 on the shaft f, a roll 9 engaging said groove, a bell-crank lever 8, 8' which is supported on a pivot 7 and to the arm 8 of which said roll is attached, and a rod 6 connepting the lever arm 8 with the said valve 5 The manner of operation of the device is as follows When the parts 6, a, g, i, n, 0 and p are moving downwardly, they take with them the cylinder 9 that constitutes, together with the piston 1", the compressed-air cushion or the cushioning device proper respectively, the compressed air present above the piston being now displaced back into the air vessel to through the bores t and u and the pipe 1). The sheet-metal h is, thus, being drawn over the die m counter to the pressure of the compressed air, this pressure being that requisite for holding yieldingly fast the rim of the blank it between the drawing ring 9 and the holding ring At the same time oil is sucked into the space below the pistonthrough the flexible pipe 2 and the now open valve 1.

When then the drawing punch is again moved upwardly, the cylinder 9 tends to follow it quickly and in a jerky manner under the action of the compressed air whereby the drawing tools 2' and 9 might possibly be injured. Such a-detrimental consequence is, however, prevented by the opposing action of the liquid previously sucked into the space below the piston and retained therein, as the valve is now automatically closed and the valve 5 is still closed at the commencement of the upward movement of the drawing punch while the roll 9 is moving in the portion 10 of the guide groove 10, 10. Only after the drawing punch has been moved upwardly for a certain length of way and the roll 9 has entered into the portion 10 of the guide groove, the rod 6 is lowered whereby the valve 5 is opened and the pressure in the space above the piston r (the compressed air streaming back into this space from the receptacle c0) is able to move the cylinder 9 upwardly, in that the liquid present below the piston is driven back through the pipe 4 into the oil receptacle'3. The members 30, 0, 'n, and 2' follow the upward movement of the drawing punch without any possibility for this latter to strike against the drawing ring, and the roll 9 enters into the portion 10 of the guide groove whereby the valve 5 is closed by the members provided for this purpose, as described.

In the modified sheet-metal drawing press shown in Fig. 2 the drawing die m is attired to the drawing punch a and reciprocates, thus, together with it, whereas the drawing ring 9 is firmly secured to the table Z0 of the press. The blank holding member 2' is an equivalent for the blank holding ring 71 of Fig. 1; it is also in the present modified case supported from below by a compressedair cushioning device. The supporting members are formed by bolts n, a pressing plate 0 and piston rods 8 which are reciprocated vertically in cylinders g suspended from the lower portion of the foot of the press by means of a girder g and rods g Each of the piston rods is provided with two pistons a" which reciprocate in cylinder chambers that are separated from one another by a partition wall 9 The air vessel to communicates through a pipe 4; and bores u of the piston rods with the cylinder spaces below the pistons r. The space C1 above the upper piston r of the middle cylinder communicates with the receptacle 3 containing the locking liquid through a valve 1 and a pipe 2, as well as through a pipe 4 which is also provided with a valve 5 controlled from the crank-shaft of the press practically in the same manner as has been described with respect to Fig. 1.

B1 denotes a rigid (not yieldingly or elastically supported) blank holder which is attached to the blank holding ram B2 and is also in known manner reciprocated vertically, just as the drawing ram that is guided in it. h denotes the skelp or blank.

The manner of operation of this constructional form of the press is as follows:

When the drawing punch a and the blank holding ram B2 are moved downwardly, the blank holder B1 holds theblank it fast upon the drawing ring 9, and now the drawing die m commences to draw the piece of sheetmetal through said ring, the holder 71 which is subjected to the action of the cushioning device serving as holding-on member. While together with the holder or holding-on member 2' the pistons 1* are moved downwardly, locking liquid is sucked into the space O1 above the piston r of the middle cylinder, that liquid preventing, when the drawing ram is again moved upwardly and the valve 5 has been closed, the piston rods 8 from following immediately that upward movement. If the piston rods were able to do that, the blank it which (with the constructional form of the press now dealt with) is still held fast by the blank holding member B1 at the time of the commencement of the upward movement of the drawing ram, were subjected to the risk of being destroyed.

The valve 1 and the pipe 2 (Figs. 1 and 2) may, under circumstances, be dispensed with.

I claim:

1. In a sheet-metal drawing press, aoushioning device for the blank holder, comprising a piston and a cylinder closed at both ends and enclosing said piston, said piston and cylinder being one fixed and the other movable and means connecting the movable one of these members operatively with said blank holder; a source of fluid under pressure, a duct connecting one of the spaces in said cylinder with said source of a fluid under pressure; a receptacle containing a liquid; a

duct connecting said liquid receptacle and the other space of the said cylinder; and a controlled valve in said liquid duct.

2. In a sheet-metal drawing press, a cushioning device for the blank holder, comprising a stationary piston and a movable cylinder enclosing said piston, closed at both ends and being operatively connected with said blank holder; a source of fluid under pressure, a duct connecting the space above said piston with said source of fluid under pressure; a receptacle containing a liquid, a duct connecting said liquid receptacle and the s ace below the said piston; and a controlle said liquid duct.

3. In a sheet-metal drawing press, a cushioning device for the blank holder, compris ing a stationary cylinder closed at both ends and a piston movable in said cylinder and being operatively connected with said blank holder; a source of fluid under pressure, a

valve in duct connecting the space below the piston with said source of fluid under pressure; a receptacle containing a liquid; a duct between said liquid receptacle and the space above the said piston, and a controlled valve in said liquid duct.

4:. In a sheet-metal drawing press, a cush ioning device for the blank holder, comprising a piston and a cylinder closed at both ends, enclosing said piston, and means connecting one of these members operatively with said blank holder; a source of fluid under pressure, a duct establishing communication between one of the spaces in said cylinder and said source of fluid under pressure; a receptacle containing a liquid; a duct establishing communication between said receptacle andthe other space of the said cylinder; a valve in said duct; a cam disk driven by the press, and means for transmitting motion from the cam of said disk to said valve so as to control it thereby.

5. In a sheet-metal drawing press, a cushioning device for the blank holder, comprisin a piston and a cylinder, closed at both ends, enclosing said piston, and means connecting one of these members operatively with said blank holder; a. source of fluid under pressure, a duct establishing communication between one of the spaces in said cylinder and said source of fluid under pressure; a receptacle containing a liquid; a duct establishing communication between said receptacle and the other space of the said cylinder; a valve in said last named duct; a disk driven by the press and having a lateral groove consisting of two portions of different radii; a roll running in said groove; a doublearmed lever, to one arm of which said roll is attached; and a connection between the other arm of said lever and said valve.

, In testimony whereof I aflix my signature.

OTTO KuHNER. 

